 public class Example4_13 {

  public static void main(String args[]) {

      Circle circle = new Circle();

      circle.setRadius(196.87);

      Tixing lader = new Tixing(3,21,9);

      Student zhang = new Student();

      System.out.println("zhang计算圆的面积：");

      double result=zhang.computerArea(circle);

      System.out.println(result);

      System.out.println("zhang计算梯形的面积：");

      result=zhang.computerArea(lader);

      System.out.println(result);

   }

}




